FIG. 3 is a diagram illustrating an optical structure of a solar simulator according to the related art.
As shown in the drawing, generally, after collecting light emitted from a light source (not shown) to be close to an optical axis using an integrator 4 for uniform irradiation where an incident angle θ1 and an emission angle θ2 are equally designed, the light is converged by a collimation lens 5, thereby obtaining emission light having high parallelism.
In this case, a parallelism angle φ of the light emitted from the collimation lens 5 can approximate to φ≈a tan (r/f). However, r indicates a circumradius of the integrator 4, and f indicates a focal distance of the collimation lens 5.
In the related art, in the above structure, in order to increase a parallelism angle of an emission light beam (decrease φ), a method where the focal distance f of the collimation lens is set to be large has been used.    Patent Document 1: Japanese Patent Application Laid-Open No. 2002-189192    Patent Document 2: Japanese Patent Application Laid-Open No. 2002-116501    Patent Document 3: Japanese Patent Application Laid-Open No. 2001-042432